The present embodiments relate to a stand for medical imaging or engineering (e.g., an X-ray stand) including a device that compensates for distortions caused by weight.
Stands such as those used in medical imaging (e.g., X-ray stands) may have a vertical arm and a horizontal bracket that is supported on the vertical arm. The vertical arm may be a telescopic tube assembly having a length that may be varied in a vertical direction, for example. The functional component to be supported by the stand (e.g., an X-ray source or X-ray detector) is then supported on the horizontal bracket. The bracket may likewise be adjustable in length, and may also be rotatable about a vertical axis and a horizontal axis. The bracket is aligned as precisely as possible horizontally (e.g., level).
If a different orientation of the bracket is desired (e.g., an orientation that is other than precisely level but nonetheless has a horizontal orientation component), the same applies accordingly. The bracket is to be aligned as precisely as possible in the desired orientation in each case. For the sake of simplicity and irrespective of the alignment that is actually desired, reference is therefore made in the following to a horizontal bracket. Horizontal bracket denotes a bracket having an alignment that is precisely horizontal or a bracket having an alignment that has at least a horizontal orientation component.
The force due to weight of the functional component that is supported on the bracket, and the horizontal distance of the component from the vertical arm, produce a torque that is exerted on the vertical arm by the horizontal bracket. The magnitude of this torque depends on the distance in a horizontal direction of the functional component, which represents a lever. The magnitude of the torque also depends on the mass of the functional component.
The stand may be distorted by the force due to weight of the functional component and the torque that is generated thereby. As a result of the torque loading of the bracket, the extension of the tubular assembly follows a path that is no longer perfectly vertical, but is slightly inclined. Since the bracket is securely connected to the telescopic tube assembly, the bracket is tilted slightly out of the horizontal orientation. The horizontal bracket may be bent by the force due to weight of the functional component. The suspension or support of the component in the vertical arm may be deflected by the torque. The distortion ultimately results in unwanted deflection from the horizontal of the horizontal bracket and any functional component that is supported thereon.
The horizontal bracket is therefore to be returned to the desired horizontal orientation (e.g., nutation) by a suitable configuration (e.g., nutational adjustment). If the torque of the bracket changes (e.g., due to movement of the axes (vertical and horizontal adjustment, rotation) and corresponding masses and the consequently varying lever arms), the alignment is to be reset every time. In this case, the nutational adjustment is set via setting screws, discs, wedges or the like. In practice, frequent resetting is very resource-intensive and is often not possible at all. Therefore, in many cases, an average value is set, and the deviations are simply accepted.
The publication U.S. Pat. No. 5,818,638 A1 discloses a jib arm for supporting an optical apparatus. Unwanted deformation of the jib arm may occur due to the weight of the optical apparatus. In order to counteract such deformation, sensors are provided for the measurement thereof. The sensors are controlled by a kinematic system including multiple parts and multiple joints.
The publication DE 10 2012 201 857 A1 discloses a C-arm X-ray device including a mobile C-arm with multiple axes. Unwanted deformation of the C-arm may occur due to the dead weight and mechanical vibrations during certain movements. In order to be able to compensate for this deformation, optical sensors based on, for example, lasers are attached to both ends of the C-arm. The sensors allow precise measurement of current changes to the respective position. Based on the the position measurements, unwanted changes may be counteracted by correcting the C-arm.